Put 260 g corn flour, starch, sugar, egg, 1 pinch of salt and butter in cubes in a bowl. Knead with your hands to a smooth dough. Cover and chill for about 1 hour.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Line two baking trays with baking paper. Dust the work surface with some corn flour. Roll out the dough thinly on top, approx. 3 mm. Cut out 25-30 circles with wavy edges (approx. 5.5 cm Ø) and 25-30 circles with wavy edges (outside approx. 5.5 cm Ø; inside approx. 2 cm Ø). Knead the dough again and again, if necessary cool, roll out and cut out.
Spread the dough circles and curls on the baking trays and bake one after the other in a hot oven for about 9 minutes until golden brown.
Cool the biscuits on the trays, then carefully place them on a cake rack and let them cool down. Warm up the jam. Spread the cookie circles with it. Place the circles on top and let them set. Dust with icing sugar.